The invention relates to a measure for reducing noise in motorcycles. For this purpose, a motorcycle having an engine and an exhaust pipe connected thereto, together with a motorcycle rear wheel swingarm are proposed, the latter having an integrated resonator connected to the exhaust pipe.
Ever more stringent noise regulations for motorcycles, in particular the internal combustion engine in operation, make it necessary to constantly develop new measures for reducing the noise level emitted by the motorcycle. In principle, the noise level is limited by the rear muffler, but without additional measures muffler volumes would in the future have to be made significantly larger in order to be able to adhere to the noise levels. However, a larger rear muffler is not desirable, for two reasons. Firstly, on motorcycles rear mufflers are one of the main design elements and therefore must not exceed a predefined size. Secondly, larger rear mufflers increase the weight and take up more overall space, which on motorcycles is something to be avoided in any event.
The use of resonators interacting with the exhaust pipe is known in the state of the art in automobiles. Here a sheet metal body, which acts as resonator, is attached to a branch on the exhaust pipe. Such a solution is not feasible on motorcycles, since the arrangement of an additional, external resonator on the exhaust pipe would be unacceptable both from visual and functional standpoints.
Against this background, the object of the invention is to provide a possible means of reducing the noise level of a motorcycle during operation, while allowing unmodified use of the existing rear mufflers.
This and other objects are achieved by a motorcycle in which the rear wheel swingarm comprises an enclosed cavity, which is in fluid connection with the exhaust pipe by a connecting element. The cavity integrated into the motorcycle rear wheel swingarm in this way serves as resonator, which is capable of reducing the engine noise level from the exhaust system by at least two decibels.
The motorcycle rear wheel swingarm is advantageously formed as a hollow-chamber profile, preferably as a cast aluminum welded construction, in order to meet the requisite demands in terms of lightweight construction. In such a hollow motorcycle rear wheel swingarm a predefined area is provided as an enclosed cavity, which acts as an acoustic resonator. The cavity integrated into the swingarm therefore constitutes a resonance cavity. It is particularly advantageous here if the cavity is formed as a Helmholtz resonator, in which natural vibrations are excited by sound waves when the frequency of part of the sound in the exhaust pipe coincides with the natural frequency of the quantity of air present therein. For each engine and its associated exhaust system it is possible, by adjusting the cavity volume and the length and diameter of the connecting element, to set the required frequency range in which the resonator is intended to be effective. Here, hot exhaust gas does not flow directly through the resonator itself; instead a standing column of air in the connecting element oscillates together with the quantity of air in the resonator.
In a preferred embodiment, a temperature-resistant hose, for example a flexible metal hose or a temperature-resistant elastomer hose, is used as the connecting element. The connecting element is preferably of a flexible design and capable of compensating for relative movements between the rear wheel swingarm and the exhaust pipe. The connecting element is advantageously connected to the cavity in the rear wheel swingarm in close proximity to the axis of rotation of the swingarm, in order to minimize relative movement during compression and rebound.
The connecting element or the temperature-resistant hose is fixed both to the cavity of the motorcycle rear wheel swingarm and to the exhaust pipe by connection fittings formed on each of them, onto which the hose can be pushed and secured/fixed by use of fixing clamps.
A beneficial effect of the cavity or resonator integrated into the rear swingarm is obtained if the connecting element or the hose is connected to the exhaust pipe upstream of the rear muffler and downstream of the catalytic converter, viewed in a direction of flow of the exhaust gas. This design is also arrived at by extending the exhaust pipe along the rear swingarm, before it opens into the rear muffler.
For adjustability of the frequency range of the cavity acting as resonator, the latter has a volume of 1000 to 3000 cm3, preferably 1800 to 2600 cm3 for standard commercial motorcycles. In an advantageous embodiment the length of the connecting element is 120 to 250 mm, more preferably 150 to 200 mm. In an advantageous embodiment the diameter of the connecting element is 30 to 40 mm, more preferably 30 to 35 mm. The respective values may be varied and adjusted in order to afford the best possible sound-reducing effect on the respective engine, exhaust pipe and rear muffler system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.